1. Field Of The Invention
The present invention relates generally to remote control of downhole tools, and more particularly, but not by way of limitation, relates to a surface system for providing automated and precise control of the well annulus pressure for use in generating control signals to communicate with a tool located downhole.
2. Description Of The Prior Art
Traditionally, downhole tools such as those utilized in drill stem testing of oil and gas wells have been controlled either by physical manipulation of the pipe string which carries the tools or by changing the pressure applied to a column of fluid standing in the well, with that pressure being directly mechanically applied to a power piston of the tool so as to move an operating element of the tool. This second mode of operation includes those tools which are directly operated by changing well annulus pressure which is communicated with a power piston of the tools, or so-called annulus pressure responsive tools.
More recently, the development of downhole tools including programmed electronic controllers has made possible the use of remote controlled tools which may receive command signals transmitted from a remote command station, located at the earth's surface, through any one of several means to a receiver contained in the tool. The programmed electronic controller then causes the operating element of the tool to be actuated through any one of several types of operating systems in response to the remotely received command signal.
One system which has been proposed for remote communication with such a preprogrammed remote control downhole tool is the use of pressure signals applied to the well annulus. The existing systems typically present at a well site for control of pressure on the well annulus are relatively crude. A series of rig pumps are communicated through a rig manifold with the well annulus. A bleed-off line communicates the well annulus with a mud tank or mud pond. The pressure applied to the well annulus is typically observed simply by visually observing a pressure gauge connected to the inlet to the well annulus. Control of well annulus pressure by applying pressure with rig pumps and bleeding off pressure to the mud tank is relatively crude and is subject to pump surging and vibration.